By Stephen Collinson

CNN

WASHINGTON (CNN) -- Donald Trump became the 45th President of the United States Friday during a time-honored inauguration ceremony that encapsulated the peaceful transfer of power that is a hallmark of American democracy.

On a raised platform on the flag-draped West Front of the Capitol, Trump placed his left hand on one Bible that dates from his childhood and another that belonged to Abraham Lincoln and raised his right hand in the air as he promised to preserve, protect and defend the Constitution.

Under gray skies and in front of a crowd stretching most of the way from the Capitol toward the Washington Monument, Trump took the oath from Chief Justice John Roberts with the new first lady Melania Trump by his side.

Trump revived some of the hardline rhetoric from the campaign during his inaugural address.

"This American carnage stops right here and stops right now," Trump said with Obama looking on.

"We assembled here today are issuing a new decree to be heard in every city, and in every foreign capital and in every hall of power," Trump said. "From this day forward, a new vision will govern our land, from this day forward it's going to be only 'America first! America first!'"

"A new national pride will stir out souls, lift our sights and heal our divisions," Trump said, saying that whether people are black or white they still bleed the same red blood of patriots.

And he told Americans listening to the address: "You will never be ignored again."

Former Presidents George W. Bush and Bill Clinton also attended the ceremony. Hillary Clinton, who Trump defeated in the November election, was also in the audience in a show of support for national unity and the peaceful transfer of presidential authority.

The swearing-in was one of many traditions that began unfolding early Friday morning. Trump and his family attended a private worship service at St. John's Church, known as the church of presidents. The Obamas greeted Trump and the new first lady, Melania Trump, at the North Portico of the White House before hosting them for tea.

Earlier in the morning, Barack Obama wrote a letter to Trump and left it on the Resolute Desk in the Oval Office, as outgoing presidents typically do for their successors. As Obama left the Oval Office for the final time, he was asked if he had any words for the American people. "Thank you," Obama said.

The customs and symbolism that are playing out -- from Trump's ride to the Capitol with Obama to the First Couple's dance at an inaugural ball -- are familiar. But the circumstances of this inauguration -- the 58th in the nation's history -- could hardly be more unconventional.

When the presidential primary season began nearly a year ago, few thought Trump could survive the battle for the Republican nomination -- much less beat Clinton to win the presidency. He will be the oldest president sworn in for a first term and the first president with no previous diplomatic, political or military executive experience. But his populist campaign deeply resonated with Americans who were fed up with Washington's political class and felt left behind in the globalizing economy.

Day of ceremony

Trump began a day of ceremony Friday morning by attending the traditional inauguration day worship service. When they arrived at the White House, Melania Trump brought a gift for the Obamas in a blue box wrapped in a bow, which the President handed into an aide before returning for a photo.

In what is always a poignant moment, the former President Obama and his family left Capitol Hill on a helicopter bound for Andrews Air Force base for a farewell ceremony before taking one last flight on the presidential jet. The Obamas are heading to Palm Springs, California, for a vacation.

Trump is attending a joint congressional inaugural luncheon in the Capitol before heading back to the White House for the inaugural parade. In the evening, Trump and the new first lady will attend two inaugural balls, part of the stripped down inaugural festivities that aides say are meant to stress that the new president is eager to get to work.

Trump's supporters, who sent him to Washington to rip up political norms and thwart the establishment, are thrilled as he assumes power. The crowds started streaming towards the National Mall as dawn broke, with many people wearing Trump's distinctive red "Make America Great Again" baseball caps.

But millions of Americans are also anxious, owing to the abrasive tone of Trump's campaign and fears over the consequences of his strongman leadership style.

Trump has vowed to tear up US trade deals that he says disadvantage US workers, confront a rising China and improve estranged relations with Russia, despite allegations that Moscow interfered in the election.

He has set high expectations for his presidency by promising to return jobs to US shores and reviving the manufacturing industry. He has pledged to crush ISIS and introduce tough new vetting on immigrants from countries where there is terrorist activity, raising fears of discrimination against Muslims.

He is promising to build a wall on the southern border, to crack down on undocumented migrants and to gut the financial and environmental regulations that are at the center of the Obama administration's legacy.

National unity

New presidents typically use the inaugural address -- viewed by a huge crowd fanned out on the National Mall and millions of television viewers -- to issue a call for national unity and ease the wounds of divisive elections. They typically remind Americans of the values and the history that binds them and of the nation's historic mission.

Trump, so far, has done little to reach out to his foes since November.

"He is still talking as if he is the insurgent candidate rather than the President-elect," said Robert Rowland, an expert on presidential rhetoric at the University of Kansas. "Historically, presidents who are effective use inaugural addresses to heal the wounds of the campaign, to talk about what it means to be an American, to discuss shared values and lay out their political principles to come across as a strong not vain leader."

CNN's Kevin Liptak and Sara Murray contributed to this story